Several present day aircraft have fuel systems that incorporate removable fuel bladders or cells. For example, UH-60 BLACK HAWK.RTM. helicopters (BLACK HAWK is a registered trademark of the Sikorsky Aircraft Division of United Technologies Corporation) and derivatives thereof utilize a pair of removable primary fuel cells mounted in side-by-side cavities in the helicopter fuselage. These helicopters are primarily designed for military and other applications wherein the helicopter may be subjected to gunfire. Major design constraints imposed upon such helicopters include ballistic survivability and ease of maintainability. Removable fuel cells are utilized to enhance ballistic survivability and maintainability.
Removable fuel cells may be fabricated from a hybrid composition, e.g., a natural or synthetic elastomeric polymer such as rubber and fibrous material that is vulcanized to net shape. Fuel cells fabricated from such a hybrid composition possess a good strength-to-weight ratio, are resistant to abrasion and impact damage, are compatible with aviation fuels, and facilitate design optimization to meet ballistic survivability requirements. In addition, fuel cells may be fabricated from such a hybrid composition to embody sufficient rigidity to satisfy a requirement to be self-supporting when empty (to facilitate hardware interconnection to fuselage structure), and concomitantly possess sufficient flexibility to be collapsible to the extent necessary to facilitate removal (and replacement) thereof.
Removable fuel cells enhance the maintainability of the aircraft. If the fuel cell experiences projectile damage as the result of gunfire, the fuel cell may be removed and replaced with an undamaged fuel cell. Removal and replacement greatly facilitates maintainability as opposed to built-in fuel tanks which would require extensive maintenance rework to either: (1) repair the damaged fuel cell in situ; or (2) remove and replace the damaged fuel cell.
However, the prior art procedures for the removal and replacement of the primary fuel cells of some variants of the UH-60 BLACK HAWK.RTM. helicopter are difficult, labor intensive, and time consuming, and present safety concerns, all of which adversely impact the maintainability of the helicopters. The fuel cells are difficult to remove and install due to the structural configuration of the fuselage cavities housing the fuel cells and the space constraints associated therewith. For example, some UH-60 BLACK HAWK.RTM. helicopters incorporate non-removable bulkheads that define the fuselage cavities for the main fuel cells. The fuel cells are accessible for removal and replacement, but the access space 122 to accomplish removal and replacement is extremely limited. For example, a space of about twenty-nine inches in height by about forty inches in width is available for removing the main fuel cell via the aircraft cabin of the UH-60A BLACK HAWK.RTM. helicopter (see FIG. 3).
While the fuel cells of the UH-60 BLACK HAWK.RTM. helicopter are sufficiently flexible to facilitate collapse thereof for removal, the inherent rigidity thereof, in conjunction with limited access thereto, poses a problem in collapsing the fuel cells for removal. FIGS. 1A, 1B illustrate the prior art removal procedure for the fuel cells 100 of the UH-60 BLACK HAWK.RTM. helicopter. The inherent rigidity of the fuel cell 100 results in the fuel cell being self-supporting in the fuselage cavity 120, i.e., the walls of the fuel cell 100 are in abutting engagement with the walls of the fuselage cavity 120. Thus, removal of the fuel cell 100 requires that the fuel cell 100 be collapsed before removal.
To collapse a self-supporting fuel cell 100, the fuel cell 100 must be first broken away from the walls of the fuselage cavity 120. With reference to FIG. 1A, straps 140 are threaded through accessible ports in the fuel cell 100 and interconnected to rings 124 mounted to an internal aircraft beam 126 by means of hooks 142 and ratcheting devices 144. The straps 140 are tensioned by operation of the ratcheting devices 144, the tensioning of the straps 140 causing the fuel cell 100 to break away from the fuselage cavity 120 and to be suspended within the fuselage cavity 120.
Once the fuel cell 100 is suspended with the fuselage cavity 120, a second set of straps 146 and ratcheting devices 148 are disposed around the periphery of the fuel cell 100 as illustrated in FIG. 1B. The ratcheting device 148 are operated to tension the straps 146, causing the collapse of the fuel cell 100. Once the fuel cell 100 has been collapsed to a height commensurate with the access space 122, the fuel cell 100 is manually removed through the access space 122.
The inherent rigidity of the fuel cell 100 and the limited access space 122 available for removal of the fuel cell 100, necessitates the use of three to four personnel to sufficiently collapse and remove the fuel cell 100 utilizing the procedure described in the previous paragraphs. The limited access space 122 increases the risk of injury to such personnel. The procedure described hereinabove is both manpower intensive and time consuming, and thus adversely affects the maintainability of the helicopter.
A need exists for a simplified method for removing fuel cells from the fuselage cavity of aircraft, particularly helicopters. The method should be compatible with the structural configuration and characteristics of the fuel cells presently incorporated in helicopters and the limited space available to access the fuel cell. The method should facilitate the collapse of the fuel cell under such circumstances, and should reduce the manpower required, the time required, and risk of injury in collapsing and removal of the fuel cell.